Disposable blood pressure transducer and monitor interface

ABSTRACT

A medical blood pressure transducer that provides an identifier to a monitor that conveys characteristics of the transducer. The monitor can use the information to decide whether to function, or in calibration of the system. The transducer may be part of a disposable blood pressure monitoring system, and may include two transducers closely-spaced to provide two separate but identical outputs. In this way, the transducer may be connected to both a patient monitor and a cardiac output monitor at the same time measurements from a single line can be simultaneously supplied to two separate monitoring devices (for example a patient monitor and a cardiac output monitor). The identifier for the transducer may be circuitry, specifically a resistance/capacitance (RC) combination that possesses a characteristic time constant.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/558,160, filed Sep. 11, 2009, entitled “Disposable Blood PressureTransducer and Monitor Interface”, and is a continuation of U.S.application Ser. No. 10/888,332, entitled “Disposable Blood PressureTransducer and Monitor Interface” filed Jul. 8, 2004, which is herebyincorporated herein in its entirety, by reference.

FIELD OF THE INVENTION

The present invention relates generally to pressure transducers formedical use and, more particularly, to a disposable blood pressuretransducer and associated monitor interface.

BACKGROUND OF THE INVENTION

When diagnosing and treating various bodily ailments, such as withpatients suffering from shock or cardiovascular problems, medicalpersonnel often find it desirable to measure and/or monitor a patient'sblood pressure. Advantageously, by measuring and/or monitoring the bloodpressure of these and other types of patients, medical personnel arebetter able to detect blood flow difficulties and other cardiovascularproblems at an early stage. As a result, the use of blood pressuremeasurement and monitoring may increase the likelihood that a patientcan be successfully treated and/or provided with needed emergencyassistance.

A variety of methods are currently used for measuring and/or monitoringblood pressure. For example, medical personnel frequently use variousindirect blood pressure measurement techniques, such as measuring apatient's blood pressure by using a pressure cuff and a stethoscope. Inaddition, blood pressure measurements are often made using a number ofdirect measurement and monitoring techniques. Notably, when diagnosingand/or treating critically ill patients, such direct techniques aregreatly preferred over any of the indirect techniques. Direct bloodpressure measurement and monitoring techniques are generally accurate towithin about one percent, and facilitate the continuous monitoring of apatient's blood pressure on a beat-to-beat basis. Direct blood pressuremonitoring also enables the rapid detection of a change incardiovascular activity, and this may be of significant importance inemergency situations.

In direct, or invasive, blood pressure monitoring systems a catheter isinserted into a patient's circulatory system with the end of thecatheter having an opening to the blood stream, typically in a major orperipheral blood vessel. First, a needle is inserted into a peripheralblood vessel. For example, if it is desired to monitor arterial bloodpressure, the needle may be inserted into the radial artery. If, on theother hand, venous blood pressure is to be monitored, the needle may beinserted into the antecubital, radial, jugular, or subclavian veins.Once the needle is properly inserted, a special catheter is threadedthrough the needle and into the blood vessel until the tip of thecatheter is positioned at the particular point within the body at whichit is desired to make the blood pressure measurement. Then, with thecatheter in place, the needle may be withdrawn.

An I.V. set attaches to the proximal end of the catheter protruding fromthe patient so that a solution flows through the catheter and into thepatient. The I.V. solution provides a fluid “column” through whichpressure pulses are transmitted, and a pressure transducer positionedalong the fluid column monitors those pressure pulses. Generally, thepressure transducer consists of a dome that functions as a reservoir forthe I.V. fluid. The dome includes a resilient diaphragm that attaches toan electrical transducer. The transducer senses pressure fluctuations inthe diaphragm and converts them into electrical signals which thentransmit through a cable to a monitor for amplification and display. Inmodern systems a single silicon chip comprises both the pressurediaphragm and the measuring circuitry of the pressure transducer. Sincesuch silicon chips are cheaply mass-produced, the total cost of pressuretransducers is reduced to the extent that the transducer becomeseconomically disposable. The cable includes a connector so that thetransducer and associated portion of the cable can be discarded afteruse, whereas the mating connector and cable hard-wired to the monitorcan be reused. Such disposable blood pressure transducers (DPTs) are thestandard of care in the OR, ICU or CCU.

Due to the separable nature of the transducer and monitor, differenttransducers may be connected to any one monitor, as long as the cableconnectors are compatible. However, transducers from different sourcesmay exhibit different performance characteristics and may requirespecific calibration and/or signal processing or conditioning.Unfortunately, the environments of the OR, ICU or CCU are ill-suited forrapid recognition and registration of disparate components of pressuremonitoring systems, and safety concerns necessitate the least amount ofsuch preparation be involved.

Furthermore, pressure data are often required by two separate monitoringdevices, such as a patient monitor and a cardiac output monitor, or apatient monitor and an aortic balloon pump. Typically, an arterial lineis placed in the patient and a DPT connected to a patient monitor isused for pressure monitoring. Instead of invasively setting up a secondarterial line and DPT, the signal from the first DPT may be supplied toa second monitor via the patient monitor. However, this “piggyback”connection may introduce pressure monitoring errors from delays anddistortion of the signals.

Despite a relatively mature market for disposable medical pressuretransducers, there remains a need for a “smart” transducer that wheninterfaced with the appropriate monitoring device ensures accuracy.There is also a need for a simpler and more reliable system fortransmitting the pressure signal to multiple instruments.

SUMMARY OF THE INVENTION

The present invention provides a pressure monitoring system thatfacilitates rapid recognition, registration and/or conditioning of adisposable blood pressure transducing device by an associated monitor,and reduces the amount of such preparation involved. Further, thedisposable blood pressure transducing device embodies “smart” technologysuch that an identifier that characterizes the blood pressuretransducing device is sensed by a signal receiving device, which allowsthe signal receiving device to appropriately condition the signal andhelps improve safety.

One aspect of the invention is a medical fluid pressure sensing systemhaving a pressure transducing device that comprises a pressure-sensitivetransducer and an identifier. The pressure-sensitive transducer iscapable of externally measuring fluid pressures and converting thosepressures into electrical signals. The identifier characterizes thepressure transducing device. The system further includes a signalreceiving device adapted to communicate with the pressure transducingdevice and capable of sensing the identifier and therefore thecharacteristics of the pressure transducing device when placed incommunication therewith.

In an exemplary system, the pressure transducing device is a fluidpressure transducing device which further comprises a housing having aconduit in which fluid may enter. The pressure-sensitive transducer ismounted in the housing for measuring fluid pressures in the conduit andconverting those pressures into electrical signals. Desirably, the fluidpressure transducing device also has an electrical connector connectedto the pressure transducer for transmitting the signals. Consequently,the signal receiving device is adapted to physically and electricallycommunicate with the connector and receive the electrical signals and iscapable of sensing the identifier and therefore the characteristics ofthe fluid pressure transducing device when placed in communication withthe connector. In the preferred embodiment, the pressure-sensitivetransducer directly senses fluid pressure.

In one embodiment, the identifier introduces an electrical signature tothe signals such that the signals and signature can be recognized by thesignal receiving device. The electrical signature may be a time- orfrequency-based feature. The physical makeup of the identifier may beselected from a group consisting of the following:

-   -   a combination of a resistor, a capacitor, and/or an inductor;    -   a memory chip;    -   a reference voltage/current;    -   an electro-magnetic signature;    -   an active or passive switch which can be electrically,        mechanically, optically, or magnetically triggered; and    -   an optical identifier.

Preferably, the identifier is provided in electrical circuitry. Forinstance, the electrical circuitry may comprise a resistance/capacitance(RC) combination that possesses a characteristic time constant. In sucha configuration, the pressure transducing device may further include anelectrical connector in communication with the pressure transducer fortransmitting the signals, wherein the connector includes electricalcontact pins and a capacitor bridging two of the pins that provides thecapacitance in the RC combination. Consequently, the signal receivingdevice is adapted to physically and electrically communicate with theconnector and is capable of sensing the identifier and therefore thecharacteristics of the pressure transducing device when placed incommunication with the connector. The signal receiving device mayinclude decision-making circuitry that will only permit functioning ofthe system depending on a determination of the time constant. In onedesirable embodiment, the decision-making circuitry will only permitfunctioning of the system if the time constant is within 20% of areference value.

Another aspect of the present invention is a medical fluid pressuretransducing device including a housing having a conduit in which fluidmay enter. A pressure-sensitive transducer mounts in the housing formeasuring fluid pressures in the conduit and converting those pressuresinto electrical signals. An electrical connector connects to thepressure transducer for transmitting the signals. An electricalidentifier characterizes the type of fluid pressure transducing device.Desirably, the pressure-sensitive transducer directly senses fluidpressure.

The identifier may introduce an electrical signature to the signals thatcan be recognized by a signal receiving device adapted to communicatewith the connector. The electrical signature may be a time- orfrequency-based feature. The physical makeup of the identifier may beselected from a group consisting of the following:

-   -   a combination of a resistor, a capacitor, and/or an inductor;    -   a memory chip;    -   a reference voltage/current; and    -   an electro-magnetic signature.

Preferably, the electrical identifier comprises a resistance/capacitance(RC) combination that possesses a characteristic time constant. In sucha configuration, the connector includes electrical contact pins and thetransducer includes a capacitor bridging two of the pins that providesthe capacitance in the RC combination. The electrical identifier ideallycomprises circuitry on the housing, the transducer, the cable, or theconnector.

A still further aspect of the invention is a dual fluid pressuretransducing device, comprising an in-dwelling catheter and an externalhousing connected to the catheter having a conduit in which fluid mayenter, the fluid therefore being placed in communication with a lumen ofthe in-dwelling catheter. Two pressure sensors mount in the housing formeasuring fluid pressures in the conduit and converting those pressuresinto electrical signals. An electrical connector is in communicationwith each pressure transducer for transmitting the signals.

In the exemplary dual fluid pressure transducing device, the pressuresensors directly sense fluid pressure. The device may further include astopcock assembly interposed between the housing conduit and thein-dwelling catheter for opening the conduit to the atmosphere andproviding a reference pressure in a fluid column defined within theconduit at a particular elevation, the pressures sensed by the twopressure sensors being the same along the fluid column.

In a preferred embodiment, the assembly of one of the pressure sensorsand associated connector includes an identifier that characterizes thetype of pressure sensor. In such an arrangement, the two connectors maybe differently colored. The housing may also include a single snap tabfor permitting flow through the conduit and generating a square pressurewave within the fluid in the conduit that can be detected by the twopressure sensors.

The present invention also provides a method of measuring fluid pressurefrom a location within a patient. The method includes the steps of:

-   -   inserting a catheter into a body vessel or cavity;    -   providing an external housing connected to the catheter having a        conduit in which fluid may enter, the fluid therefore being        placed in communication with a lumen of the in-dwelling        catheter, the housing having at least one fluid pressure sensor        mounted therein for measuring fluid pressures in the conduit and        converting those pressures into electrical signals; and    -   transmitting signals representing two measurements of fluid        pressure from the at least one fluid pressure sensor to at least        one signal receiving monitor.

In a preferred method, there are two fluid pressure sensors, and thesignals representing two measurements of fluid pressure derive one fromeach sensor. An electrical connector may be associated with each fluidpressure sensor, wherein the method further includes connecting the twoconnectors to different signal receiving monitors.

In a preferred method, the assembly of one of the fluid pressure sensorsand associated connector may include an identifier that characterizesthe type of pressure sensor. With such a configuration, the methodincludes detecting the identifier with the monitor and adjusting signalprocessing accordingly. The signals representing two measurements offluid pressure may be transmitted to two different signal receivingmonitors. In a specific application, the fluid is blood and one monitoris a patient monitor and the other is a cardiac output monitor.

Further understanding of the nature and advantages of the invention willbecome apparent by reference to the remaining portions of thespecification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of an exemplary disposable medicalpressure transducing device of the present invention as typicallymounted on a support pole for use;

FIG. 2 is a perspective view of the exemplary disposable medicalpressure transducing device with its cables stretched out straight;

FIGS. 3A-3D are front, top, end and section views of the exemplarydisposable medical pressure transducing device;

FIG. 4 is a longitudinal sectional view of a housing of the exemplarydisposable medical pressure transducing device seen in perspective;

FIG. 5 is a longitudinal sectional view of a housing of the exemplarydisposable medical pressure transducing device seen in elevation; and

FIG. 6 is a circuit schematic of a connector pin interface between theexemplary disposable medical pressure transducing device and a signalreceiving device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an improved disposable blood pressuretransducing device (DPT) that carries with it an identifier that can bedetected by an associated monitor such that the monitor recognizes thecharacteristics of the device. If the monitor recognizes the type of DPTas compatible, it can proceed with the pressure measurement. Ideally themonitor is calibrated to work best with particular DPTs, and theidentifier provides the “signature” for those transducers that areoptimal. More generally, the identifier tells the monitor which type ofDPT it is receiving signals from and therefore what, if any, signalconditioning is required.

The term “identifier” is used herein to broadly encompass features ofthe DPTs that can be sensed or otherwise recognized by the monitor.Electrical circuitry is probably the most efficient means to identify aDPT because it can be built in to the existing circuitry and sensed viathe DPT connector pins, without need to physically modify the monitorconnector. For instance, a resistance/capacitance (RC) combination thatpossesses a characteristic time constant can be built into the DPTelectrical circuit and the monitor can easily be configured tointerrogate the DPT connector for that time constant. Other identifiersare listed below and the reader should be cognizant that any of theseinterfaces between the DPT and monitor may be used.

In the context of the present invention, a blood “pressure transducer”is a sensor capable of sensing or determining a blood pressure, such asthe fluid pressure of blood within a line leading out of the body froman arterial catheter, and converting such pressure to a signal that canbe communicated to a monitor/display. A number of such blood pressuretransducers are known, and none are specifically excluded from the scopeof the invention. Blood pressure can be sensed directly (i.e., viadirect physical contact with blood) or indirectly (i.e., optically or ata pulse point through the skin). For example, catheter-based fluidpressure transducers in direct contact with arterial blood are presentlyaccepted as standard practice in the OR, ICU or CCU, thoughless-invasive techniques such as external piezo-electric sensors incontact with the skin are available. It should be understood that theaspect of the invention that permits identification of the particularsensor/transducer by the monitor is not limited to direct or indirectmeasurement techniques, or to fluid pressure monitoring for that matter.Although blood pressures are the target parameter measured in theexemplary embodiments, certain aspects of the “smart” interface betweenthe transducer and monitor may also be desirable for systems thatmeasure other bodily fluids, such as cerebro-spinal fluid.

Now with reference to FIGS. 1, 2 and 3A-3D, the main components of anexemplary disposable blood pressure transducing device (DPT) 20 will bedescribed. FIG. 1 shows the DPT 20 mounted vertically to a mountingbracket 22 on a support pole 24, as is common in hospital settings. TheDPT 20 includes a housing 30, a pair of cables 32 a, 32 b extending fromone end of the housing and terminating in electrical connectors 34 a, 34b, and a two-port stopcock assembly 36 on the opposite end of thehousing. The DPT 20 is seen stretched out in a linear fashion in FIG. 2,and has an exemplary length from the farthest connector 34 b to thestopcock assembly 36 of about 1 foot (30 cm), though longer cables maybe used. Although not shown in these figures, an internal flow channelin the stopcock assembly 36 leads to a short length of tubing 38situated on a top side of the housing 30 opposite a mounting plate 40.The mounting plate 40 engages L-shaped walls in the mounting bracket 22,as seen in FIG. 1, such that the tubing 38 faces outward from themounting bracket.

Not shown in FIGS. 1-3 are the associated components of the pressuremonitoring system that connect to the DPT 20. Typically, a signalreceiving device such as a patient or cardiac output monitor includescables and connectors that mate with the connectors 34 a, 34 b andreceive electrical signals indicative of fluid pressure detected by theDPT 20. Various monitors are available for this purpose and will not befurther described herein, except below in the context of an interfacefeature of the present invention that permits identification by themonitor of the characteristics of the DPT 20. Additionally, anin-dwelling catheter that provides the particular fluid to be measuredattaches to one of the ports of the stopcock assembly 36, typically theport in line with the DPT 20 that is fitted with a luer connector. Manycatheters may be used for pressure monitoring, and the specifics arewell known in the art. It should be noted, however, that the EdwardsTruWave® Disposable Pressure Transducer is adapted to be combined withan arterial blood sampling line, such as the VAMP® (Venous ArterialBlood Management) kits also available from Edwards Lifesciences.

Furthermore, the term “catheter” as used herein refers to any elongatedstructure for accessing a body cavity such as a blood vessel andprovides a conduit through which fluid may pass. In the preferredembodiment, a saline solution provides a fluid “column” through whichpressure pulses from the catheter lumen are transmitted, and a pressuretransducer positioned along the fluid column monitors those pressurepulses. Devices for providing such access include cannulas, needles,sheaths, introducers, and other such structures, typically tubular.

Now with reference to FIGS. 4 and 5, internal details of the DPT 20 areillustrated. The housing 30 actually comprises several components thatare bonded or otherwise coupled together. The tubing 38 is formed by afirst tube section 50 a of a first manifold 52 a, a second tube section50 a of a second manifold 52 b, and a shunt member 54. A common lumenleads through the first and second tube sections 50 a, 50 b and shuntmember 54. The housing 30 further includes first and second transducerenclosures 56 a, 56 b each having a large lower wall and a number ofsmaller walls upstanding therefrom that cooperate with and connect tooppositely-directed walls formed in the first and second manifolds 52 a,52 b. The engaging walls may be bonded with adhesive or ultrasonicwelding or the like. Each of these parts is typically made of moldedmedical grade plastic.

The first and second transducer enclosures 56 a, 56 b are substantiallyidentical as is their respective cooperation with the first and secondmanifolds 52 a, 52 b. As a result, two similar transducer chambers 60 a,60 b provide space for two pressure sensors or transducers 62 a, 62 bthat are located adjacent openings 64 a, 64 b to the lumens of the firstand second tube sections 50 a, 50 b, respectively. The transducers 62 a,62 b mount in blocks 66 a, 66 b of insulating material and are placed inelectrical communication with the cables 32 a, 32 b via wires 68. Fluidpressure within the common lumen of the housing tubing 38 can thereforebe sensed at two closely spaced-apart locations. Because of the closespacing between the transducers 62 a, 62 b, typically no more than about3 inches (8 cm), the two pressure waveforms being detected are notsignificantly different. Indeed, the stopcock assembly 36 is interposedbetween the housing conduit 38 and the in-dwelling catheter (not shown),and is opened to the atmosphere and providing a reference pressure in asaline fluid column defined within the conduit at a particularelevation. That is, as seen best in FIG. 1, the stopcock assembly 36 isnormally positioned at the same elevation on the support pole 24 as thepatient's heart. This equilibrates the “pressure heads” of the fluidcolumn within the conduit 38 to that of the patient's heart. When thestopcock 36 is closed, the pressures sensed by the two pressuretransducers 62 are the same along the fluid column in the conduit 38.

One particularly useful blood pressure transducer 62 a, 62 b iscurrently sold by Edwards Lifesciences of Irvine, CA, under the tradename Edwards TruWave® Disposable Pressure Transducer, and includes amonolithic silicon pressure sensor employing a four-terminal resistiveelement formed in a thin monocrystalline silicon diaphragm Acceptablesilicon pressure sensors are commercially available from Motorola, Inc.More details on acceptable pressure transducers are disclosed in U.S.Pat. No. 4,539,998, and Re 33,518, the disclosures of both of which arehereby expressly incorporated herein by reference. A particularlypreferred silicon pressure sensor is a sensor which includes atemperature compensation circuit for compensating the sensed pressure inthe fluid based upon the temperature of the fluid and correcting suchsensed pressure. Such a silicon pressure sensor is commerciallyavailable from Motorola, Inc. as SPX-1001D pressure sensors.

The first and second tube sections 50 a, 50 b are similarly sized butnot identical because of the provision of a snap tab flush device 70 inthe second. The snap tab flush device 70 includes a resilient tab 72that has a distal end 74 normally occluding a port into the second tubesection 50 b. A plug 76 closes off the second tube section 50 b adjacentthe port, and the port leads to a by-pass channel 78. Pulling the tab 72lifts the distal end 74 from the port and permits fluid to flow from thesecond tube section 50 b to the by-pass channel 78. This flushes thedevice and also permits measurement of a square pressure wave created bythe transient of the “snap” back of the tab 72. A square wave testpattern may be desirable for calibration of the transducers 62 a, 62 b.

The first and second tube sections 50 a, 50 b are in fluid-flowcommunication with an inlet port 80 provided on the stopcock assembly36. The housing 30 further includes an outlet port 82. Both the inletand outlet ports are structured to enable the affixing of tubing theretoand are axially aligned to provide a substantially unimpeded flow paththrough the housing 30. The inlet port 80, outlet port 82 and tubing 38provide a fluid-flow pathway through which fluid can be administered toa patient while simultaneously permitting the monitoring of pressurewaves along the fluid pathway.

In use, a catheter (not shown) is positioned within a body vessel orcavity and connected to intermediate tubing or directly to the inletport 80. An I.V. set attaches to the proximal end of the catheterprotruding from the patient so that a solution flows through thecatheter and into the patient. Vents (not shown) in the first and secondtube sections 50 a, 50 b permit an I.V. solution (typically saline) tofill the tube sections and provide a fluid “column” through whichpressure pulses are transmitted. Connectors of one or more monitors(also not shown) are placed in communication with the transducers 62 a,62 b via the electrical connectors 34 a, 34 b. Pressure measurements canthen be taken as desired when the system is calibrated.

The provision of two transducers 62 a, 62 b and associated cables 32 andconnectors 34 permits the DPT 20 to be connected to different monitorshaving different functions. For instance, a patient monitor that merelydisplays blood pressure can be connected to the first connector 34 a andtransducer 62 a, while a cardiac output monitor may be connected to thesecond connector 34 b and transducer 62 b. The cardiac output monitorincludes software that utilizes the pressure information in an algorithmthat outputs cardiac volumetric flow data. In this way, a second DPT andsecond catheter is rendered unnecessary. Furthermore, some existingsystems process a single pressure signal through both a patient monitorand a cardiac output monitor, which may be limited to a few selectedpatient monitors and increases pressure monitoring error through delaysand distortion of the signal passed to the patient monitor. Further, theclinician must often ignore the Directions For Use of the patientmonitor. It will be apparent therefore that the dual DPT 20 provides asignificant tool to the critical care doctor.

As mentioned, the present invention provides an “identifier” in the DPT20 that relays information to a connected signal receiving device suchas a monitor concerning the characteristics or source of the DPT. Thisinformation can be used as a decision switch for overall functioning ofthe system, or can tell the monitor specific technical details about theDPT that aid in calibration and operation. In the context of disposableblood pressure transducers, the identifier permits the signal receivingdevice or monitor to appropriately condition the signal, which thereforehelps improve safety. That is, various DPTs have different signal outputcharacteristics depending on the type and physical specifications of thetransducer, among other factors, and the signal typically requiresamplification, filtering, and other such conditioning. Knowledge of thesignal output characteristics via detection of the identifier instantlynotifies the monitor of the proper conditioning to apply. It isconceivable that a monitor may be programmed to operate with numerousDPTs with different characteristics, requiring the monitor to applydifferent conditioning depending on the particular DPT. Of course, eachDPT would have to have an identifier that can be detected by themonitor.

FIG. 6 illustrates a schematic connector pin interface for the DPT 20and an associated monitor 90 that enables the monitor to “see” whetherthe DPT is compatible, and determine the DPT characteristics. Theexemplary “identifier” comprises a resistance/capacitance (RC)combination that possesses a characteristic time constant. Specifically,a capacitor 92 is connected between the 4^(th) and 5^(th) pins 94 of theDPT 20, a resistor 96 extends between an excitation pin 1 and pin 5. Themonitor 90 includes software or other decision-making hardware thatdetects the time that it takes for the capacitor 92 in the RC circuit tocharge. With an understanding of the specific resistance and capacitancevalues, the monitor 90 can decide whether the time equals an expectedtime, or falls within an acceptable time window, preferably about 20%plus or minus of the expected time. If the time to charge the capacitor92 falls within the acceptable range, the system proceeds with thepressure monitoring. If not, the system shuts down and displays an errormessage, or otherwise indicates the non-compliance. Alternatively, themonitor 90 may include a programmed decision tree that processes theincoming pressure signals according to which type of DPT is detected,which is determined by the identifying time constant.

Numerous ways in which to incorporate an identifier into the DPT 20 arecontemplated, all of which would require a complementary detector in themonitor 20. For instance, the identifier could be any combination of aresistor, a capacitor, and/or an inductor that is energized orinterrogated by an electrical connection with the monitor to send anidentifiable electric signal. These circuit components could reside intransducer 62 circuit itself, the cable 32, the connector 34, or evenwithin the monitor 90. Alternatively, the identifier could comprise amemory chip (e.g., EEPROM) in the DPT 20 which is accessed by themonitor 90 upon electrical connection therebetween. More simply, the DPT20 may contain a source of power such as a small battery which deliversa reference voltage/current to the monitor 90. It should be noted thatthe signature signal or modification of the standard DPT output could betime-based or frequency-based features that are recognizable by themonitor 90 (e.g., wireless auto-ID dot on DPT).

Other than circuit identifiers, an electro-magnetic signature inherentin a magnetic strip card, for example, could be used. In that case, themonitor 90 would require some mode of reading the strip card. Active orpassive switches which can be electrically, mechanically, optically, ormagnetically triggered (e.g. relays, FETs, transistors, switches), couldalso be used. For instance, a pressure switch in the monitor connectorcould be triggered by connection of the two connectors, whereasconnection to a different DPT would not activate the switch. Onespecific example of such a switch is an insulated contact on the DPT 20or monitor 90 connector that is pierced or broken and completes acircuit when the two connectors are engaged. Along the same lines, ascheme of optical identification via color, reflectivity, scattering,grating, or opto-chemical (e.g., barcode) may define the identifier.

Another desirable aspect of the present invention is the ability of theDPT 20 to produce two separate though identical pressure signals. This“dual DPT” enables pressure measurements from one arterial line to besimultaneously supplied to two separate monitoring devices (for examplea patient monitor and a cardiac output monitor, or a patient monitor andan aortic balloon pump). This avoids the need to place another arterialline in the patient and connect another DPT for pressure monitoring, andreduces pressure monitoring error inherent in delays and distortion ofsignals that are supplied to a second monitor via the patient monitor.

In the exemplary embodiment, as seen in FIGS. 1-5, the dual DPT 20includes two pressure transducers 62 a, 62 b within one housing 30, thetransducers being fluid pressure sensors that directly sense bloodpressure within a single length of tubing 38. Each transducer 62 a, 62 bhas separate wires 68 extending therefrom and continuing in separatecables 32 a, 32 b that terminate in separate connectors 34 a, 34 b. Oneconnector 34 a, 34 b can thus be placed in communication with a matingconnector for a patient monitor and the other in communication with amating connector for a cardiac output monitor. Preferably, only theassembly of the transducer 62, wires 68, cable 32, and connector 34 thatcommunicates with the cardiac output monitor includes the “identifier”mentioned above, so that the monitor can detect the type of transducerand apply the proper signal conditioning. The connectors 34 a, 34 b maybe differently colored to distinguish them and signify which one isassociated with the identifier.

It should be understood that there are various ways to structure the DPT20 to produce two output signals, and the present invention is intendedto cover all such structures. For example, instead of the seriesconfiguration shown, the transducers 62 a, 62 b may be mounted inparallel with a bifurcation or “Y” in the fluid line. Alternatively, asingle transducer assembly or manifold may be used with multiplesensors. Multiple sensors can be spaced axially in series along thefluid line, or at the same “height” around the circumference of theconduit. Circuitry may be provided to allow multiple instruments (inputsignals) to read one sensor (e.g. multiplexing or signal matching). Inall these cases it should be understood that the sensors are external tothe body and not mounted on the in-dwelling catheter. Furthermore, asmentioned above, the sensors may or may not be fluid pressuretransducers, and may or may not directly measure blood pressure. Onespecific alternative is a dual optical sensor that senses blood pressurefrom a distinct pulse point where the arteries are near enough to thesurface of the skin, such as in the neck or wrist.

While the foregoing is a complete description of the preferredembodiments of the invention, various alternatives, modifications, andequivalents may be used. Moreover, it will be obvious that certain othermodifications may be practiced within the scope of the appended claims.

What is claimed is:
 1. A method of sensing fluid pressures in a patientusing a fluid pressure sensing system, the method comprising:establishing communication between an identifier of the system and asignal receiving device of the system, wherein the identifiercharacterizes a pressure transducing device of the system and comprisesa resistance/capacitance (RC) combination possessing a characteristictime constant within 20% of a reference value; and comparing, usingdecision-making circuitry of the signal receiving device, thecharacteristic time constant and the reference value and permitting ornot permitting additional processing by the system based on a result ofthe comparison.
 2. A method of claim 1, further comprising measuring thepatient fluid pressures and converting the patient fluid pressures intoelectrical signals using the pressure transducing device.
 3. A method ofclaim 2, wherein the additional processing includes the measuring fluidpressures and converting the fluid pressures into electrical signals 4.A method of claim 2, wherein the additional processing includesreceiving, with the signal receiving device, the electrical signals fromthe pressure transducing device.
 5. A method of claim 2, wherein theadditional processing includes displaying the electrical signals.
 6. Amethod of claim 1, wherein the additional processing includes receivingcharacteristics of the pressure transducing device.
 7. A method of claim1, wherein not permitting additional processing is based on the resultsof the comparison including the time constant exceeding a range of thereference value.
 8. A method of claim 7, wherein the range is greaterthan 20%.
 9. A method of claim 1, wherein the additional processingincludes establishing communication between the pressure transducingdevice and the signal receiving device.
 10. A system for measuring fluidpressures in a patient, the system comprising: a pressure transducerconfigured to measure patient fluid pressures; an identifier including aresistance/capacitance (RC) combination possessing a characteristic timeconstant within 20% of a reference value, the identifier characterizingthe pressure transducer; and a signal receiver configured to communicatewith the identifier, the signal receiver configured to compare thecharacteristic time constant to the reference value and permit, or notpermit, additional processing by the system based on a result of thecomparison.
 11. A system of claim 10, wherein the pressure transducer isfurther configured to convert the patient fluid pressures intoelectrical signals and communicate the electrical signals to the signalreceiver.
 12. A system of claim 11, wherein the additional processingincludes converting the fluid pressures into electrical signals.
 13. Asystem of claim 11, wherein the additional processing includesreceiving, with the signal receiver, the electrical signals from thepressure transducer.
 14. A system of claim 10, wherein the additionalprocessing includes receiving characteristics of the pressuretransducer.
 15. A system of claim 10, wherein not permitting additionalprocessing is based on the results of the comparison including the timeconstant exceeding a range of the reference value.
 16. A system of claim15, wherein the range is greater than 20%.
 17. A system of claim 10,wherein the additional processing includes establishing communicationbetween the pressure transducer and the signal receiving device.